Design Patterns

Design Patterns

In software engineering, a design pattern is a general repeatable solution to a commonly occurring problem in software design. A design pattern isn't a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations.

Uses of Design Patterns

Design patterns can speed up the development process by providing tested, proven development paradigms. Effective software design requires considering issues that may not become visible until later in the implementation. Reusing design patterns helps to prevent subtle issues that can cause major problems and improves code readability for coders and architects familiar with the patterns.

Often, people only understand how to apply certain software design techniques to certain problems. These techniques are difficult to apply to a broader range of problems. Design patterns provide general solutions, documented in a format that doesn't require specifics tied to a particular problem.

In addition, patterns allow developers to communicate using well-known, well understood names for software interactions. Common design patterns can be improved over time, making them more robust than ad-hoc designs.

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Difference between var and dynamic in C#

Introduction

The type keyword 'var' was introduced in C# 3.0 (.NET 3.5 with Visual Studio 2008) and the type 'dynamic' was introduced in C# 4.0 ( .NET 4.0 with Visual Studio 2010). Let us see the difference between these two

Background

Variables declared with var are implicitly but statically typed. Variables declared with dynamic are dynamically typed. This capability was added to the CLR in order to support dynamic languages like Ruby and Python.

This means that dynamic declarations are resolved at run-time, var declarations are resolved at compile-time. 

Table of difference 

var	dynamic
Introduced in C# 3.0	Introduced in C# 4.0
Statically typed – This means the type of variable declared is decided by the compiler at compile time.	Dynamically typed - This means the type of variable declared is decided by the compiler at runtime time.
Need to initialize at the time of declaration. e.g., var str=”I am a string”; Looking at the value assigned to the variable str, the compiler will treat the variable str as string.	No need to initialize at the time of declaration. e.g., dynamic str; str=”I am a string”; //Works fine and compiles str=2; //Works fine and compiles
Errors are caught at compile time. Since the compiler knows about the type and the methods and properties of the type at the compile time itself	Errors are caught at runtime Since the compiler comes to about the type and the methods and properties of the type at the run time.
Visual Studio shows intellisense since the type of variable assigned is known to compiler.	Intellisense is not available since the type and its related methods and properties can be known at run time only
e.g., var obj1; will  throw a compile error since the variable is not initialized. The compiler needs that this variable should be initialized so that it can infer a type from the value.	e.g., dynamic obj1; will compile;
e.g. var obj1=1; will compile var obj1=” I am a string”; will throw error since the compiler has already decided that the type of obj1 is System.Int32 when the value 1 was assigned to it. Now assigning a string value to it violates the type safety.	e.g. dynamic obj1=1; will compile and run dynamic obj1=” I am a string”; will compile and run since the compiler creates the type for obj1 as System.Int32 and then recreates the type as string when the value “I am a string” was assigned to it. This code will work fine.